Patients with substance use disorders require a multi-pronged therapeutic approach incorporating behavioral interventions and medications; however, cocaine use disorder, a major public health concern in the U.S., is without an FDA-approved medication. At the core of severe cocaine use disorder is an undeniable compulsion toward drug-seeking and -taking that has been linked to cocaine-induced, long-term plasticity in key brain circuits resulting in a propensity towards relapse, even after years of abstinence. Compelling preclinical evidence suggests that decreased serotonin (5-HT) 5-HT2C receptor (5-HT2CR) signaling during withdrawal from cocaine self-administration promotes relapse phenomena. Therefore, restoration of 5-HT2CR signaling capacity during the critical stages of withdrawal provides the conceptual framework for the development of pharmacotherapies to treat cocaine use disorder. We hypothesize that rationally designed positive allosteric modulators (PAMs) will selectively enhance 5-HT2CR function and provide the necessary structure-activity relationship (SAR) data required for structural optimization toward the development of neuroprobes for elucidating 5-HT2CR signaling and medications for cocaine use disorder. We aim to utilize our well-established, cell-based calcium release assay as a primary readout of positive modulation at the 5-HT2CR and establish a strategy that affords unparalleled improvements in selectivity by targeting the topologically distinct allosteric site, as opposed to the conserved orthosteric site. Our previous studies have provided several selective 5-HT2CR PAMs and established project feasibility. The project will benefit greatly from the collection of SAR data and structural optimization of novel pharmacophores that have not been extensively explored toward the goal of generating small molecule neuroprobes and preclinical candidates. The proposed innovative project will expand the current knowledge of 5-HT2CR function and has a foreseeable high impact translational value with the potential to produce a first-in-class pharmacotherapy toward the treatment of cocaine and other psychostimulant use disorders. The applicant has designed the described project and individual training plan to incorporate the necessary interdisciplinary skills and knowledge required to secure a postdoctoral appointment and to subsequently become a successful, independent investigator at the university level with a research focus on the design, synthesis, and pharmacological characterization of molecular probes and therapeutics for substance use disorders. Specifically, completion of the aims will afford the applicant with the following skills: synthetic organic and medicinal chemistry; cell culture and cell-based assays; experimental design and chemical/pharmacological characterization of small molecules; G protein-coupled receptor targeting; the fundamentals of drug discovery in the allosteric modulation, neurobiology and the psychostimulant addiction fields; preclinical models; and important skills such as project design, grant and manuscript writing, networking, teamwork, and oral presentation skills.